Vikings
Amongst the first peoples to venture into the open ocean on long journeys were the Vikings. They determined their latitude by noting the position of the Pole Star and using a notched stick or ships mast to measure its altitude, they are known to have produced altitude tables for certain stars. They also released birds which the ship would follow to land if the distance was not too great. They also had the benefit of decades of practical knowledge about wind or swell patterns, glacial reflections and the location of seaweed beds to help fix their position.
Polynesians
 Extended ocean voyages were nothing new to Polynesian peoples well before the invention of the compass, sextant or GPS, like the Vikings they relied on feedback from their environment to guide them. The sun, stars, swell patterns, landmarks and sea life could all be used to indicate position and progress along the journey. The art of long distance navigation and pacific migration are supported by the achievements of Thor Heyerdahl and the Kon-Tiki expedition in 1947, when they journeyed 4,300 miles from Peru to the Tuamotu islands in a traditional style raft.
Kon Tiki – haakonhanson
Navigation Instruments
Accurate measurement of the stars and sun combined with accurate time keeping led to truly scientific navigation based on positions stating
longitude and latitude.
Latitude was determined by comparing your position on Earth with the position of either the sun or the North Star (Polaris) this process usually required
an instrument of some kind such as a Kamal, Cross Staff or Back Staff. These were consequently superseded by the Quadrant which was suspended
from a fixed point on the boat and measured angles from the vertical. The Astrolabe had movable parts that could be used to represent the relative
positions of a number of celestial bodies. These readings were then used to determine the observers’ latitude.
Mayflower map and cross staff – oefe
The Sextant
 The sextant is undoubtedly one of the most significant advances in celestial navigation, invented around 1700 by Newton, the sextant uses two mirrors to bring the reflected image of the body down to the horizon and measure its angle to the horizon. Accuracy is the sextants most useful feature with angular measurements accurate to within 10 seconds. Navigation by sextant, in reality, is a complex process. The basic principles however are straight forward. Latitude is determined by measuring the angle between the sun and horizon at the suns highest point in the sky, usually around midday. Longitude can be determined accurately because the Earth rotates at 15° every hour (1° every 4 minutes) toward the East. This means that longitude can be calculated by using the relative time difference between your current location and the Prime Meridian.
Sextant- jojo4art
Latitude and Longitude
Pinpointing your position on a map requires knowledge of co-ordinates, known as latitude and longitude, your position is described as being at the intersection of these lines. Latitude is your position north or south of the Equator (0°). Lines, or parallels, are drawn at regular intervals around the Earth. The North Pole is at latitude 90° North and the South Pole at latitude 90° South.
 Meridians or lines of longitude, run in a North - South direction and divide the Earth into segments similar to an orange. The line of longitude designated as 0°, passes through Greenwich in London, and is known as the Prime Meridian. Longitude and latitude are the basis of all navigation and mapping. Perhaps the oldest surviving map dates from about 6200 BC and is painted on a wall in Turkey. Like its modern equivalents, it is a visualisation tool that represents geographical phenomena and their spatial relationships. Modern cartography (mapmaking) has developed to represent everything from topographical features to air and water quality. In recent years Geographic Information Systems and electronic maps have become commonplace with marine and auto navigation systems linked to satellites.
Prime Meridian - geo8
 Taking a Bearing
On a local level, positions are described by taking bearings from your position to visible landmarks and translating these onto a map. It is common practice to take at least three bearings for accuracy and triangulate the location. If using a hand compass sight along the compass at eye level toward the landmark and note the bearing toward the object, (the method of reading this will vary between compass types). Transfer a line representing the bearing onto the map for each sight, your position is at the intersection of these lines.
Hand bearing compass - Gerald 5970
Prime Meridian - geo8
Global Positioning System - GPS
GPS is the most precise navigation system available, capable of showing an exact position to within a couple of meters in any weather, 24 hours
a day. Prior to 1980 the system was only available to the US military, GPS is now used widely around the world by civilian and military organisations
as well as individuals because of its ease and accuracy.
What is GPS?  The
GPS network is a system of 24 satellites that circle the globe in very precise orbits. Each satellite orbits twice daily and transmits a signal
which is received by GPS units and used to triangulate the exact location. In common with compass bearings the unit must be locked onto, and receive
signals from at least three different satellites to obtain an accurate fix, if four or more satellites are locked on then altitude may also be
derived. Once calculated the location is displayed on an electronic map or data screen in the GPS unit either as a point or as coordinates. Speed,
distance to destination, bearings to waypoints, tracks and more can be determined using the various functions and pages available on the GPS
unit.
How It Works
The 24 orbiting satellites transmit extremely accurately timed signals, in essence each GPS receiver calculates the time difference between when a signal is transmitted and when it is received to determine its distance from the satellite.
By taking measurements to number of satellites, it is possible to determine latitude, longitude and altitude of the user. Modern GPS receivers are
extremely accurate and can utilise up to twelve satellites at any one time.
View from space - waxy poetic
 The
Satellites
The first of 24 satellites was launched in 1978, and all orbit the earth
at an altitude of approximately about 19,300 km, travelling at a speed
of 11,260km/hr. They are kept in accurate orbit by small rocket boosters
that fire periodically to keep them on track. Energy is mostly from solar
panels with small backup batteries to supply power during a solar eclipse.
The satellites are designed to last about 10 years and are replaced as
they go out of service.
12.08 - Timo
The Signal
GPS satellites transmit two low power radio signals one
civilian and one for military use. The signals travel by line of sight,
meaning that they will travel through clouds, glass or plastic but will
not penetrate solid objects such as buildings. A number of factors can
affect the accuracy by degrading the quality of the radio signal. Atmospheric
effects, signal reflection, orbital errors, receiver clock errors and
poor satellite geometry are a few of the inhibiting factors, despite
this GPS is still by far the most accurate and easy to use form of position
fixing.
Links & Documents
An overview of GPS Technology prepared by the Aerospace Corporation
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The relative positions of both the moon and stars alter by a small amount every night. Keeping track of these changes is an important aspect of navigation requiring the observer to be oriented in space and time. The simplest way to do this is to use an immovable object like a house or tree as a reference point for your observations. Stonehenge and many other ancient structures were built for this very purpose, another method is to face either north or south and watch the stars slowly rotate around the celestial poles.
Early Astronomers
The First Navigators